Hydro-chemical Characters and Ions Source of Groundwater from Qidong Coal Mine, Northern Anhui Province, China

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1 An Interdisciplinary Response to Mine Water Challenges Sui, Sun & Wang (eds) 2014 China University of Mining and Technology Press, Xuzhou, ISBN Hydrochemical Characters and Ions Source of Groundwater from Qidong Coal Mine, Northern Anhui Province, China Herong Gui, Song Chen School of Earth Sciences and Engineering, Suzhou University, Suzhou, Anhui , China Abstract Major ions were analyzed for twenty six groundwater samples collected from diverse aquifers in Qidong coal mine, northern Anhui province, China. Hydrogeochemical characters and ions sources of groundwater were discussed, the result showed that: the diverse groundwater samples have vary ions controlled by waterrock interaction, the concentrations of Cl are low for all groundwater samples, whereas the contents of SO 4 2 and HCO 3 are high with diversity degrees for groundwater. The concentrations of Na + were decreasing as follows: LA (limestone aquifer)< QA (Quaternary aquifer)< CA (Coalbearing aquifer), whereas the contents of Ca 2+ and Mg 2+ were increasing from CA to LA oppositely. Keywords groundwater, ions source, hydrogeochemstry, Qidong coal mine Introduction Deep groundwater is always reserving some information what inherit from the aquifer through the waterrock interaction over a long period of time. Thus, many studies, focusing on the groundwater quality, waterrock interaction and hydrogeochemical process have been completed, what based on the hydrochemical analyzed (Kumar et al. 2009; Ramkumar et al. 2013). All these studies had revealed regional hydrochemical process characteristics, and have important significance for the utilization of groundwater resources. Qidong coal mine is located in northern Anhui Province, China, where has abundant coal resources. The studies about hydrogeochemical and groundwater source discrimination are weak. Especially, the printed information about different statistical methods using in groundwater source identification are blank. The purpose of this study is to identify the groundwater evolution for diverse aquifers, using hydrochemical and statistical analysis. The major targets are to (1) constrain the hydrogeochemical process of groundwater for diverse aquifer, (2) recognize the ions source of groundwater. Materials and methods Qidong coal mine, belonging to Huaibei mining area, is located at northern Anhui Province, China, which constituted by about thirty couples mines (fig.1). The climate in the area is marinecontinental, with an annual average temperature of Previous research showed Qidong coal mine mainly includes three aquifers: the Quaternary aquifers (QA), Coal bearing aquifer (CA) and Limestone aquifer (LA), all the three aquifers have threat to the coal mine exploration (Gui et al. 2007). The Quaternary aquifer is constituted by yellow mudstone, sandstone and conglomerate, with a depth ranging from 280 to 300 m. The Coal bearing aquifer is characterized by mudstone, siltstone and sandstone, with a depth between 300 and 700 m. Limestone aquifers are mainly composed of limestone with clastic rocks, which belong to Taiyuan formation and Ordovician. A total twentysix groundwater samples were collected from diverse aquifers in Qidong coal mine. All the groundwater samples are as flows: seven samples from QA, eleven samples from CA and eight samples from LA. Water samples were collected via drainage holes in alleys, and then filtered through 0.45 μm poresize membrane and collected into 166

2 polyethylene bottles that had been cleaned using trace element clean procedures. All the twentysix samples were analyzed for major ions. Fig. 1 Location of study area in northern Anhui Province, China Results and discussion Major ion chemistry In general, the anion Cl, SO 2 4, HCO 3 and CO 2 3 concentrations in the groundwater range from 21 to 283 mg/l, 4 to 2064 mg/l, 188 to 630 mg/l and 0 to 93 mg/l, with averaged 211, 721, 397 and 11 mg/l, respectively. Otherwise, the cation Na +, Ca 2+ and Mg 2+ concentrations of the groundwater range from 1.0 to 940, 3.0 to 539, and 7.0 to 144 mg/l, with averaged 344, 147 and 68, respectively. The groundwater of QA is divided to NaSO 4 or NaHCO 3 type, however the LA groundwater is mainly be CaSO 4 or CaHCO 3. The geochemical data of groundwater were plotted on a Piper diagram (fig. 2), some information could be obtained. The concentrations of Cl are low for all groundwater samples, whereas the contents of SO 4 2 and HCO 3 are high with diversity degrees for groundwater collected from different aquifer. The cations also have the similar character with the anions. The most groundwater samples from coal bearing aquifer were characterized by the high concentrations of Na +, and the anions are dominated by the SO 4 2 or HCO 3. Whereas, the groundwater samples from Quaternary aquifer have higher concentrations of Ca 2+ and Mg 2+. The anions were consisted by SO 4 2 and HCO 3, which were similar with the coal bearing aquifer. The contents of Ca 2+ and Mg 2+ were dominated in the groundwater from limestone aquifer, with high concentration of SO 4 2. In conclusion, the concentrations of Na + were decreasing as follows: LA<QA<CA, whereas the contents of Ca 2+ and Mg 2+ were increasing from CA to LA oppositely. 167

3 Ions source Hydrochemistry of groundwater always influenced by such factors: recharging and waterrock interaction, the degree of waterrock interaction controlled by residence time within the aquifer (Gaillarde et al. 1999). Generally, three general processes contribute to the generation of solutes in groundwater: evaporation dissolution, carbonate dissolution and silicate weathering. As can be seen from fig. 3(A, B), the groundwater in the area is mainly controlled by silicate weathering, the evaporate dissolution and carbonate dissolution also played important role on the groundwater from QA and LA, respectively. Especially, the groundwater samples of LA were influenced by the carbonate dissolution obviously. Fig. 2 Piper diagram of groundwater from Qidong coal mine in northern Anhui province, China. Table 1 Chemical summary of groundwater samples from Qidong coal mine Na + Ca 2+ Mg 2+ SO 4 2 Cl HCO 3 Max Min Mean LA mean QA mean CA mean For the dissolution of halite in water releases equal concentration of Na + and Cl into the solution, mechanism of acquiring salinity in groundwater systems could be identified using the NaCl relationship, (Sami et al. 1992). Thus, the value Na + /Cl could be present a line and the value Na + /Cl close to one, if Na + and Cl came from halite dissolution only. However, the fig. 3C is presented different vision with Na + /Cl ratios of most samples above one. What could be implied that additional Na +,probably from other source. Generally, the additional Na + in groundwater could be originated from weathering of silicate minerals, the views could be supported by some silicate mineral could be found in the aquifer rocks. And the weathering process often along with increased HCO 3 concentrations, what are presented from Figure 3D. 168 CO 3 2

4 Fig. 3 Plots of major ion for groundwater samples in Qidong coal mine(a and B are plots of Na + normalized Ca 2+ HCO 3 and Ca 2+ Mg 2+ ; C and D are scatter of Cl Na + /Cl and (Ca 2+ +Mg 2+ )(HCO 3 +SO 4 2 ); E and F are scatter of (Ca 2+ +Mg 2+ )HCO 3 and(ca 2+ +Mg 2+ )SO 4 2 ) The source of Ca 2+ and Mg 2+ in groundwater could be determined from the ratio of (Ca 2+ +Mg 2+ )/HCO 3. The ratio would be about 0.5, if Ca 2+ and Mg 2+ come in groundwater only from dissolution of carbonates in the aquifer, or from the weathering of pyroxene and amphibole (Meybeck et al.1987). The ratio of the groundwater samples in the area are ranging from 0.09 to 9.7, with average value 2.66 (fig. 3E), revealing that the balance between concentration of Ca 2+ +Mg 2+ and HCO 3 are changed by some reason. The strong positive correlation between Ca 2+ +Mg 2+ and SO 4 2 are presented by fig. 3F, suggesting that sulfate dissolution could be important for the extra Ca 2+ +Mg 2+. In additional, the low 169

5 (Ca 2+ +Mg 2+ )/HCO 3 ratio of few groundwater samples could be the result of Ca 2+ +Mg 2+ depletion by cation exchange. In a word, the groundwater samples in the area are mainly controlled by silicate weathering, especially in the Coal bearing aquifer. However, the dissolution of evaporate and carbonate are also played an important role on groundwater from QA and LA, respectively. Sulfate dissolution could be important for the extra Ca 2+ +Mg 2+, for the best correlation between Ca 2+ +Mg 2+ and SO 2 4. Conclusions (1) The concentrations of Cl are low for all groundwater samples, whereas the contents of SO 2 4 and HCO 3 are high with diversity degrees for groundwater. The cations also have the similar character with the anions. In conclusion, the concentrations of Na + were decreasing as follows: LA<QA<CA, whereas the content of Ca 2+ and Mg 2+ were increasing from CA to LA oppositely. (2) The groundwater samples in the area are mainly controlled by silicate weathering, especially in the Coal bearing aquifer. Otherwise the dissolution of evaporate and carbonate also played important role on groundwater from QA and LA, respectively. Sulfate dissolution could be important for the extra Ca 2+ +Mg 2+. Acknowledgements The study was supported by the National Nature Science Foundation of China ( , ), the Anhui province Department of education Natural Science Foundation (KJ2013A249) and the Program for Innovative Research Team in Suzhou University (2013kjtd01). References Gaillarde J, Dupré B, Louvat P, Allègre CJ (1999) Global silicateweathering and CO 2 consumption rates deduced from the chemistry of large rivers. Chemical Geology 159: 230 Kumar M, Kumari K, Singh UK, Ramanathan AL (2009) Hydrogeochemical processes in the groundwater environment of Muktsar, Punjab: conventional graphical and multivariate statistical approach. Environ Geol 57: Meybeck M (1987) Global chemical weathering of surficial rocks estimated from river dissolved loads. American Journal of Science, 287: Ramkumar T, Venkatramanan S, Anithamary I, Ibrahim SMS (2013) Evaluation of hydrogeochemical parameters and quality assessment of the groundwater in Kottur blocks, Tiruvarur district, Tamilnadu, India. Arab J Geosci 6: Sami K (1992) Recharge mechanisms and geochemical processes in a semiarid sedimentary basin, Eastern Cape, South Afirca. Journal of Hydorlogy 139: 2748 Sun LH, Gui HR, Chen S (2011) Rare earth element geochemistry of groundwater from coal bearing aquifer in Renlou coal mine, northern Anhui Province, China. Journal of Rare Earths 29: